Since the past, a choke coil for a power supply circuit is known that is composed of a plate-shaped magnetic body core, a coil element that is wound around the magnetic body core, and two terminals that are formed on both end portions of a surface of the magnetic body core and respectively electrically connected to both ends of the coil element (for example, refer to Japanese Laid-open Patent Publication No. 11-243021). In the choke coil, a lead wire is connected to a terminal by high-temperature soldering, and the terminal is adhered to the surface of the magnetic body core by an electrically conductive adhesive such that the lead wire is interposed between the terminal and the magnetic body core.
When a winding of a transformer is connected to an external terminal, to increase the reliability of the connecting section, the winding of the transformer and the external terminal are sometimes bonded by a solder or the like after an end portion of the winding is wound around the external terminal. In such instances in which bonding which accompanies winding is performed, slack in the winding of the transformer is no longer present and tension is generated when the winding is wound around the external terminal.
When mounting of the transformer device is performed while the tension is still being generated, for example, during a reflow process, the winding of the transformer may become disconnected as a result of thermal contraction after thermal expansion of the winding of the transformer.